Method for Production of Metal by Molten-Salt Electrolysis and Method for Production of Titanium Metal

ABSTRACT

A method for production of metal by molten-salt electrolysis is a method for production of metal by molten-salt electrolysis which is performed by filling molten salt of a metal chloride in an electrolysis vessel having an anode and a cathode, and a molten salt which reduces solubility of the metal in the molten salt is used.

TECHNICAL FIELD

The present invention relates to the recovery of metal from a chloridethereof, and in particular, relates to a method for production of metalby molten-salt electrolysis. Furthermore, the present invention relatesto a method for production of titanium metal using the metal produced bythe method.

BACKGROUND ART

Conventionally, titanium metal, which is a simple substance, is producedby the Kroll method, in which titanium tetrachloride is reduced bymolten magnesium to obtain sponge titanium, and various kinds ofimprovements have been made to reduce the cost of production. However,since the Kroll method is a batch process in which a set of operationsis repeated noncontinuously, there is a limitation to its efficiency.

To overcome this problem, a method in which titanium oxide is reduced bycalcium metal in molten salt to obtain titanium metal directly (seeWO99/064638 and Japanese Unexamined Patent Application Publication No.2003-129268), one in which an EMR method in which a reducing agentcontaining an active metal such as calcium or an active metal alloy isprepared, and one in which a titanium compound is reduced by electronsfrom the reducing agent to yield titanium metal (see Japanese UnexaminedPatent Application Publication No. 2003-306725) have been proposed. Inthese methods, calcium oxide, which is a by-product of the electrolyticreaction, is dissolved in calcium chloride, and molten-salt electrolysisis performed to recover and reuse calcium metal. However, since thecalcium metal generated during the electrolytic reaction is in a liquidstate and is highly soluble in calcium chloride, it dissolves easily inthe calcium chloride, and there has been a problem in that the yield ofthe metal is reduced.

As explained above, there has been a problem in that it has beendifficult to recover metal such as calcium metal efficiently by aconventional method.

DISCLOSURE OF THE INVENTION

The present invention has been completed in view of the abovecircumstances, and an object of the present invention is to provide amethod for production of metal by molten-salt electrolysis, in whichmetal used for reducing, such as an oxide or chloride of titanium metal,is efficiently recovered, and another object of the present invention isto provide a method for production of titanium metal in which the metalproduced by the method is used.

The method for production of metal by molten-salt electrolysis of thepresent invention is a method for production of metal by molten-saltelectrolysis which is performed by filling molten salt of a metalchloride in an electrolysis vessel having an anode and a cathode, and amolten salt which reduces solubility of the metal in the molten salt isused.

In the method for production of titanium metal of the present invention,the metal produced in the above-mentioned method is used as a reducingagent of titanium tetrachloride.

By the method for production of metal by molten-salt electrolysis of thepresent invention, since the solubility of the metal in the molten saltis reduced, the metal that is deposited is difficult to dissolve in themolten salt. Therefore, the metal can be effectively recovered.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual cross sectional diagram showing the electrolysisvessel used in the molten salt electrolysis of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are explained below with referenceto the drawings. Here, a case in which the metal is calcium metal, themetal chloride is calcium chloride, and the chloride added to reduce themelting point of the electrolysis bath of the molten salt of the presentinvention is potassium chloride, is explained.

FIG. 1 shows a desirable embodiment of the apparatus structure toperform the present invention. In FIG. 1, reference numeral 1 indicatesan electrolysis vessel, and an electrolysis bath 2 mainly containingcalcium chloride is filled in the vessel. The electrolysis bath 2 isheated to a temperature above the melting point of calcium chloride by aheater, which is not shown, so as to be maintained in a meltedcondition. As the electrolysis bath 2, a bath of a mixture of calciumchloride and potassium chloride is used. Not only can the melting pointof the electrolysis bath 2 be reduced by adding potassium chloride tocalcium chloride, but the solubility of calcium metal in theelectrolysis bath 2 can also be reduced.

Reference numeral 3 indicates an anode and reference numeral 4 indicatesa cathode, and they are immersed in the electrolysis bath 2. Between theanode 3 and the cathode 4, for example, a dividing wall 5 made ofgraphite is arranged.

Starting the electrolysis of the electrolysis bath 2 by connecting theanode 3 and cathode 4 to a direct current power supply, which is notshown, chloride ions in the electrolysis bath 2 are attracted to theanode 3 and donate electrons, forming chlorine gas 6, which is expelledfrom the system. Calcium ions are attracted to the cathode 4 and acceptthe electrons, forming calcium metal 7, which is deposited on thesurface of the cathode 4.

It is desirable that the temperature of the electrolysis bath 2 be notless than 650° C. which is a eutectic temperature of calcium chlorideand potassium chloride, and that it be not more than 1000° C. In thecase in which the target calcium metal is required to be recovered in asolid state, the temperature of the electrolysis bath is maintained atnot less than the eutectic temperature of calcium chloride and potassiumchloride and at not more than the melting point of calcium metal (845°C.). In the case in which calcium metal is recovered in a melted state,the temperature of the electrolysis bath 2 is maintained at not lessthan the melting point of calcium metal.

The temperature of the electrolysis bath is different depending onwhether the target calcium metal is to be recovered in a solid state ora melted state, as explained above; however, the bases for improvingrecovery efficiency are the same. The upper limit is set at 1000° C.;however, in the case in which the present invention is performed at atemperature not less than the melting point of calcium metal, recoverybecomes difficult if solubility of calcium which dissolves in the moltensalt is increased. In addition, the vapor pressure of calcium metalincreases above 1000° C., and it becomes difficult to recover thecalcium metal that is generated. Therefore, in the present invention,the upper limit of the temperature of the electrolysis bath 2 isdesirably not more than 1000° C.

It is believed that the range of temperature of the electrolysis bath 2is desirably from 650° C. to 850° C. If the temperature of theelectrolysis bath 2 is less than 650° C., the electrolysis bath 2 willsolidify, as mentioned above. If the temperature of the electrolysisbath 2 is 650° C. or more, it is possible for an electrolysis bathcontaining a sufficient calcium source to be prepared, and the rate ofgeneration of calcium will be high. In addition, if the temperature is850° C. or less, the rate of dissolution of calcium in the electrolysisbath 2 will be low, and deterioration of material used for theelectrolysis vessel or the like will be low; this temperature range istherefore desirable for practicing the present invention.

The eutectic composition of the electrolysis bath 2 mentioned above is25 mol % as a ratio of addition of potassium chloride to calciumchloride. Therefore, it is desirable that potassium chloride in theelectrolysis bath 2 also be selected to be not more than 25%. It isdesirable that the amount of potassium chloride in the electrolysis bath2 be low; however, from the viewpoint of reducing the melting point ofthe electrolysis bath 2, it is desirable that the amount be higher.Therefore, the ratio of the addition of potassium chloride to calciumchloride should be determined while considering the tradeoffs.

In the case in which the present invention is performed at a temperaturenot less than the melting point of the electrolysis bath 2 and that notmore than 845° C. (not more than the melting point of calcium metal), itis possible for the calcium metal to be deposited near the electrode andto be recovered in a solid state. In the case in which the metal is notdeposited, the metal is dispersed in the bath as metal particles, andsince the specific gravity thereof is less than that of the bath, theparticles float up to the surface of the bath around the cathode. In thecase in which the metallic particles are recovered, it is possible torecover them in a mixed condition with the electrolysis bath, and as anembodiment of the present invention, a mixture of the electrolysis bathand solid metal or the metal alone can be recovered.

On the other hand, also in the case in which the electrolysis isperformed at a temperature not less than 845° C. and not more than 1000°C., the solubility of calcium metal in the electrolysis bath 2 can bereduced by controlling the concentration of chlorides added to theelectrolysis bath 2. As a result, calcium metal in a solid state ispartially deposited at the surface of an electrode and is dispersed inthe bath. On the other hand, since the specific gravity of calcium metalpartially generated in a melted state is lower than that of the bath, itwill ultimately float up near the cathode as a melted metal.

By recovering the melted metal, the present invention can be performedin the temperature range. During the recovery, since it would take along time to separate calcium metal dispersed in the bath and theelectrolysis bath 2, it is desirable that the melted calcium and theelectrolysis bath 2 be recovered in a mixed state. Apart from theserecovery methods, it is possible for the molten salt and calcium to beentirely recovered in a solid state. In the case in which the recoverymethod is performed, it is possible to use the entire range of thetemperature of the present invention.

Calcium metal deposited on the surface of the cathode 4 is partiallydissolved in the electrolysis bath 2, and calcium metal partially floatsup to the surface of the electrolysis bath. The calcium metal whichfloated up to the surface of the electrolysis bath may flow to near theanode and will be blocked by the dividing wall 5 to efficiently reducethe back reaction with chlorine gas generated at the anode 3.

Since calcium metal is soluble in calcium chloride, in the case in whicha conventional electrolysis bath consisting of calcium chloride alone isused, the calcium metal deposited will be dissolved in the electrolysisbath. However, in the present invention, since the above-mentionedchloride is added to calcium chloride to reduce the solubility ofcalcium chloride in the bath, calcium metal alone or the electrolysisbath in which calcium metal is precipitated can be efficientlyrecovered.

In addition, by determining the solubility of calcium in theelectrolysis bath at not more than 3%, calcium metal generated byelectrolysis or a bath containing a large amount of calcium metal can beefficiently recovered. The solubility of calcium metal in theelectrolysis bath is more desirably not more than 1.5%, and by selectingthe solubility, the recovery efficiency of calcium metal generated byelectrolysis can be improved further.

As a method for reducing the solubility of calcium metal in theelectrolysis bath, two methods may be considered. One is a method inwhich the content of calcium chloride is decreased and the content ofpotassium chloride, sodium chloride or calcium fluoride is increased toreduce the solubility of calcium metal, and the other is a method inwhich the temperature of the electrolysis bath 2 is reduced. By each ofthese methods, the solubility of the calcium metal in the electrolysisbath can be efficiently reduced. It should be noted that the solubilityof calcium metal can be efficiently reduced if the temperature of theelectrolysis bath is near the melting point of calcium chloride in thecase of the bath of calcium chloride alone.

Calcium metal or the electrolysis bath 2, in which calcium metal isprecipitated and recovered in this way, can be used in direct reductionof titanium oxide, for example.

In the case in which potassium chloride is added to calcium chloride at5 mol % to 50 mol %, solubility of calcium versus calcium chloride canbe reduced to a level of 0.1 % to 0.3%, in a temperature range of 650°C. to 800° C. in the electrolysis bath 2.

In addition, by adding the above-mentioned chlorides, not only can thesolubility of the calcium metal in calcium chloride be reduced, but themelting point of the electrolysis bath can also be reduced. Since themelting point of calcium chloride is 780° C. and the melting point ofcalcium metal is 845° C., calcium metal in a solid state can bedeposited on the cathode 4 in the case in which the temperature of theconventional electrolysis bath consisting of calcium chloride alone isset at 800° C. In this case, the difference between the temperature ofthe electrolysis bath and the melting point of the electrolysis bath(780° C.) is only 20° C., and since the electrolysis bath would solidifyif the temperature were to go below the melting point, it is necessarythat the temperature of the electrolysis bath be controlled precisely.

However, in the present invention, since the melting point of theelectrolysis bath 2 is reduced by mixing the above-mentioned chloridesin the electrolysis bath 2, precise control of temperature is no longerrequired, and molten-salt electrolysis can be performed reliably. Forexample, since the electrolysis bath 2 does not solidify even if thetemperature of the electrolysis bath 2 is set at around 750° C., calciummetal can be deposited in a solid state on the cathode 4. Practically,by adding potassium chloride to calcium chloride at 5 to 50 mol %,electrolysis can be performed in the electrolysis bath having atemperature about 30 to 140° C. lower than in the case of the bath ofcalcium chloride alone.

As explained, in the present invention, since calcium chloride can bedeposited in a solid state, dissolution of calcium metal in theelectrolysis bath 2 is reduced, and the yield of calcium metal can beeffectively improved.

In the case in which calcium metal is deposited in a solid state, aftera certain amount of calcium metal is deposited, supply of electric powerto the anode 3 and cathode 4 is stopped, the cathode 4 is pulled out ofthe electrolysis bath 2, and the calcium metal is scraped off to berecovered. Alternatively, the cathode is transported to a recoveryvessel, which is prepared in advance and which is not shown, and calciummetal deposited on the cathode is melted and recovered by heating therecovery vessel to a temperature not less than the melting point ofcalcium metal.

It should be noted that the mixed salt in which sodium chloride orcalcium fluoride is added, instead of the potassium chloride mentionedabove, can be used as the electrolysis bath 2. The eutectic temperatureof the mixed bath in which sodium chloride is added to calcium chlorideis 500° C. Furthermore, the eutectic temperature of the mixed bath inwhich calcium fluoride is added to calcium chloride is 670° C. In eachcase, the temperature of the electrolysis bath 2 can be effectivelyreduced compared to the case of the melting point of calcium chloride(780° C.) alone. In addition, the temperature of the electrolysis canalso be reduced, and as a result, dissolution loss of calcium metalgenerated in the electrolysis reaction of the electrolysis bath 2 canalso be efficiently reduced.

While the electrolysis of the molten salt is performed using theelectrolysis bath in which potassium chloride is added to calciumchloride, it is desirable that the voltage of the electrolysis beselected so as not to cause deposition of potassium metal. Since thetheoretical decomposition voltage of calcium chloride is 3.2 V and thetheoretical decomposition voltage of potassium chloride is 3.4 V, arange of from 3.2 V to 3.4 V is desirable. However, if the electrolysisis performed at a decomposition voltage of not less than 3.4 V,potassium metal that is produced will react with calcium chloride toproduce calcium metal. Therefore, it may not cause a substantial problemeven if the decomposition voltage is high.

If the voltage applied to the anode and cathode is increased, the amountof electricity supplied to the electrolysis vessel 1 and rate ofdeposition of metal can be increased. However, according to the increaseof the voltage applied, both surfaces of the dividing wall 5 will bepolarized. Metal is deposited on the anode-side of the dividing wall 5and chlorine gas is generated on the cathode-side of the dividing wall 5when the voltage applied reaches twice the theoretical decompositionvoltage. The chlorine gas generated on the cathode-side of the dividingwall 5 could bring the back reaction with calcium metal generated at thecathode 4, reducing the yield of calcium metal. Therefore, the voltageapplied to the anode 3 and cathode 4 is desirably an electrolysisvoltage which does not produce the polarization of the dividing wall 5.Such a range of voltages is not less than the theoretical decompositionvoltage of calcium chloride and is less than twice thereof. Practically,it is from 3.2 V to 6.4 V.

The anode used in the present invention is required to be made from amaterial which is durable when exposed to chlorine gas at hightemperature. As such a material, graphite is desirable. Not only isgraphite durable when exposed to chlorine gas at high temperature, butit is also durable in electrolysis baths at high temperature, and it hasappropriate conductivity. It is desirable that the anode be arrangedpenetrating an upper lid of the electrolysis vessel 1, which is notshown, while being immersed in the electrolysis bath 2. The surface ofthe anode 3 consisting of graphite and penetrating the upper lid can becoated with a ceramic material. Such a structure can minimize acorrosion of the graphite.

Since chlorine gas is not generated from the cathode, the cathode, atleast, can be made of a material durable to molten salt at hightemperature, such as a conventional carbon steel. In the cathode, sincethere is a possibility of generating carbide when metal is generated, asteel material having a low concentration of carbon is desirable. Thiscarbon steel is desirable since it is durable to molten salt and calciummetal at high temperatures. In addition, it is practical since it isinexpensive and durable.

The dividing wall of the present invention must be made from a materialthat is durable to calcium chloride and chlorine gas at hightemperature, similar to the case of the anode. Practically, graphite isdesirable. The dividing wall itself can be constructed of graphite, oralternatively, an inner part may be constructed of a ceramic and theouter part may be constructed of graphite, and the strength thereof athigh temperatures can be maintained for long periods.

The dividing wall is required to be dense as possible as can; however,some porosities in the wall, which do not allow penetration andmigration of calcium metal generated in the cathode 4 to the anode side,do not pose problems in conducting the present invention. Furthermore,it is not necessary for the lower edge of the dividing wall to reach thebottom part of the electrolysis vessel, and it is sufficient for thedividing wall to have a sufficient length so as not to allow calciummetal generated at the cathode 4 or a calcium chloride layer havingprecipitated calcium metal to migrate to the anode.

Chlorine gas is recovered from the system, and for example, it can beused in a chlorination reaction of titanium ore. Furthermore, calciummetal can be used in a reduction reaction of titanium oxide or titaniumchloride using molten salt to produce titanium metal. For example, itcan be used as the reducing agent of titanium tetrachloride disclosed inJapanese Unexamined Patent Application Publication No. 2005-068540, toproduce ingots of titanium metal. Alternatively, it can be used as thereducing agent of titanium metal in the FFC method in which titaniumoxide is used as a raw material disclosed in Japanese Application LaidOpen No. 2002-517613.

By using the mixed salt explained above as the electrolysis bath, themelting point of the electrolysis bath can be reduced, which brings tothe reduction of the electrolysis temperature, and as a result, thesolubility of calcium metal in calcium chloride can be reduced.Furthermore, since the ratio of calcium chloride in the electrolysisbath is decreased by using the mixed salt, the amount of the calciummetal dissolved into the electrolysis bath can be reduced compared tothe case in which calcium chloride alone is used as the electrolysisbath.

It should be noted that sodium chloride or calcium fluoride can be usedinstead of the potassium chloride mentioned above. In this case, theeutectic composition of sodium chloride to calcium chloride is 54%.Furthermore, the eutectic composition of calcium fluoride to calciumchloride is 20%. Therefore, in the case of using any of the chlorides,the electrolysis bath 2 having the above-mentioned eutectic composition,or a composition not more than that, is desirable.

In this way, by practicing the present invention, the melting point ofthe electrolysis bath can be reduced, and the solubility of calciummetal in the electrolysis bath can be reduced. As a result, the calciummetal generated according to the present invention can be efficientlyrecovered compared to the conventional methods.

EXAMPLES Example 1

Using the electrolysis vessel shown in FIG. 1, while maintaining thetemperature of the electrolysis bath consisting of calcium chloride at75 mol % and potassium chloride at 25 mol % at 650° C., and applying avoltage of 4.5 V between an anode 3 made of carbon and the cathode 4made of carbon steel, the electrolysis of the molten salt of calciumchloride is started. Accompanied by the electrolysis of the molten salt,calcium metal is deposited on the cathode in a solid state. Afterdepositing a predetermined amount of calcium metal on the cathode in asolid state, electric power supply to the positive and cathodes isstopped. After that, the cathode, having deposited calcium metal on itssurface, is transferred to a recovery vessel which is heated to atemperature not less than the melting point of calcium metal, and thecalcium metal deposited on the surface of the cathode is melted so thatit can be recovered. The ratio of the amount of calcium metal actuallyrecovered to the amount of calcium metal generated, calculated from theelectric power applied to the electrolysis bath, was 85%. It wasconfirmed that an electrolysis reaction having high efficiency could beperformed.

Example 2

Using the electrolysis vessel shown in FIG. 1, while maintaining thetemperature of the electrolysis bath consisting of calcium chloride at85 mol % and potassium chloride at 15 mol % at 730° C., and applying avoltage of 5.0 V between an anode 3 made of carbon and the cathode 4madc of low-carbon steel, the electrolysis of the molten salt of calciumchloride was started. Accompanied by the electrolysis of the moltensalt, calcium metal in a solid state floated up to the bath surfacearound the cathode. The electrolysis bath and calcium metal were drawnoff and recovered from the bath surface around the cathode. Therecovered calcium content in the electrolysis bath was measured to be50%. The amount of calcium metal generated was measured from therecovered amount and the concentration, and a ratio was calculated witha theoretical generated amount calculated from the time of electricpower supply. As a result, it was confirmed that not less than 75% ofcalcium metal was recovered. This operation was repeated, and theefficiency was improved.

Example 3

Using the electrolysis vessel shown in FIG. 1, while maintaining thetemperature of the electrolysis bath consisting of calcium chloride at85 mol % and potassium chloride at 15 mol % at 950° C., and applying avoltage of 5.0 V between an anode 3 made of carbon and a cathode 4 madeof low-carbon steel, the electrolysis of the molten salt of calciumchloride was started. Accompanied by molten-salt electrolysis, calciummetal in a melted state floated up to the bath surface around thecathode. The electrolysis bath and melted calcium metal were drawn offand recovered from the bath surface around the cathode. Melted calciumwas recovered and the concentration of calcium in the electrolysis bathwhich was recovered was measured and was 30%. The amount of calciummetal generated was measured from the recovered amount and theconcentration, and a ratio with a theoretical generated amountcalculated from the time of electric power supply was calculated. As aresult, it was confirmed that not less than 60% of calcium metal wasrecovered. This operation was repeated, and the efficiency was improved.As an additional experiment, the electrolysis bath consisting of calciumchloride at 85% and potassium chloride at 15% was maintained at 950° C.and solubility of calcium in a saturated state was measured, and it was2.8%.

Example 4

Except that 20 mol % of calcium fluoride was added to calcium chlorideinstead of potassium chloride, electrolysis tests were performed underthe same conditions as those of Example 3. Calcium metal recovered inthis Example 4 was 70% of the theoretical value.

Example 5

A molten salt in which the added ratio of potassium chloride to calciumchloride was 25 mol % was prepared, and calcium metal corresponding to10 wt % of the total of all the molten salts was added to the moltensalt to perform heating and melting testing. In the testing, the heatingtemperature was set at several levels to determine the effects on therecovery ratio of calcium metal. As a result, as shown in Table 1, therewas a tendency for the recovery ratio of calcium metal to continuouslydecreased with increasing temperature in a range of heating temperatureof 800° C. to 1000° C. However, when the heating temperature was above1000° C., a strong tendency for the recovery ratio of calcium metal todecrease was observed. The reason for this is estimated to be that boththe evaporation loss of calcium metal and the solubility of calciummetal in the molten salt are increased by increasing the bathtemperature. Furthermore, similar testing was performed in the cases ofcombinations of sodium chloride and calcium chloride, and combinationsof calcium fluoride and calcium chloride, and results similar to thosein the case of potassium chloride were obtained. TABLE 1 Unit: wt %Temperature Mixed salt 800° C. 900° C. 1000° C. 1010° C. 1050° C.CaCl₂—KCl (25) 95 70 60 45 30 CaCl₂—NaCl 97 75 65 50 40 (54) CaCl₂—CaF₂(20) 92 66 55 40 25*Values in parentheses are eutectic compositions.

Comparative Example 1

An electrolysis bath consisting of calcium chloride alone was maintainedat 900° C., a voltage of 4.5 V was applied to an anode made of carbonand a cathode made of carbon steel, so as to begin an electrolysis of amolten salt of calcium chloride. At this time, little melted calciummetal was observed at the surface of electrolysis bath. The electrolysisbath around the surface was drawn off to analyze the concentration ofcalcium metal, and the concentration of the calcium metal was 1%. Inaddition to the electrolysis examination, the solubility of calcium in asaturated state in calcium chloride at 900° C. was measured, and it was3.2%.

As explained above, metal used for reduction of oxides or chlorides oftitanium can be efficiently recovered by the present invention.

1. A process for production of a metal by molten-salt electrolysis, theprocess comprising a step of filling metal chloride in an electrolysisvessel having an anode and a cathode, wherein a molten salt whichreduces solubility of the metal in the molten salt is used.
 2. Theprocess for production of a metal by molten-salt electrolysis accordingto claim 1, wherein the metal generated by the electrolysis is recoveredalone or as a mixture of the molten salt and the metal.
 3. The processfor production of a metal by molten-salt electrolysis according to claim1, wherein the molten salt contains at least one selected from calciumchloride, potassium chloride, sodium chloride, and calcium fluoride. 4.The process for production of a metal by molten-salt electrolysisaccording to claim 1, wherein the molten salt is a mixed salt of calciumchloride with potassium chloride, sodium chloride, or calcium fluoride,and a composition of the potassium chloride, sodium chloride, or calciumfluoride versus the calcium chloride is a eutectic composition or is notmore than the eutectic composition.
 5. The process for production of ametal by molten-salt electrolysis according to claim 1, wherein themetal is calcium, potassium, or sodium.
 6. The process for production ofa metal by molten-salt electrolysis according to claim 1, wherein thetemperature of the molten salt is not less than the eutectic temperatureof a mixed salt of calcium chloride with potassium chloride, sodiumchloride, or calcium fluoride and is not more than 1000° C., and whereinthe metal generated by the electrolysis is generated alone or as amixture of the molten salt and the metal.
 7. The process for productionof a metal by molten-salt electrolysis according to claim 6, wherein thesolubility of metal in the molten salt is not more than 3%.
 8. A processfor production of titanium metal comprising a step of using the metalproduced in the method according to claim 1, as a reducing agent oftitanium tetrachloride.